1. Field of the Invention
The present invention relates, in general, to a mechanochemical process for producing fine tungsten carbide (WC)/cobalt (Co) composite powders.
2. Description of the Prior Art
With superior mechanical properties including wear resistance, hot strength and elasticitic modulus WC/Co hard metals are the most widely used for tool materials or wear-resistant parts.
Such mechanical properties of the hard metal generally depend on its chemical composition, the grain size distribution of WC, its carbon content and micro structure, and the defects it contains, such as pore, free carbons and impurities. Of them the size of WC grain and the mean free path of WC and Co are the most important variables to determine the properties of the hard metal. For example, as the WC grains in the hard metal become smaller, hardness, compressive strength, transverse rupture strength (TRS) and wear resistances are improved. In addition, the smaller the mean free path of WC and Co is, the better the mechanical properties of the hard metal. Thus, in order to improve the properties of WC/Co hard metal, it is necessary to make the size of WC grain smaller and the mixture of Co and WC more homogeneous.
Conventionally, WC/Co composite powder is prepared by sufficiently mixing tungsten (W) with carbon black in a ball-mill, and performing a heat treatment for the mixture at 1,400.degree.-1,600.degree. C. in a carbon crucible under a hydrogen atmosphere to give WC, and mixing it with Co, serving as a binder with a ball-milling. However, the ball-milling may cause detrimental impurities to be contained in the resulting powder and the strongest pulverization possible may have a limited effect in making the powder fine. Moreover, it is virtually impossible to completely mix W with carbon or WC with Co owing to the difference in their specific gravities. It is also difficult to make fine WC grain with Co by ball milling. Further, since a temperature as high as 1,400.degree. C. is required for the carbonizing reaction, the conventional method has disadvantages in the production costs when considering the facility necessary for such high temperatures and the energy consumed.